Deterioration mechanism of vegetable tanned leather revealed by proteomics and structural analysis

Abstract

Leather deterioration process and mechanism are crucial for the rescue, conservation treatment and preventive conservation of archaeological leather, however, comprehensive research in this field is scarce and urgently needed. In this work, the deterioration behavior of artificially aged vegetable-tanned sheep leathers prepared using ancient traditional tanning methods was systematically investigated from multiple perspectives. The deterioration resulted in darkening of the leather color, weight loss of up to 25 %, reduction of mechanical strength, thermal stability and a decrease in hydroxyproline content of approximately 40 %. Combining proteomics and morphology, a new model for the leather hierarchical structural deterioration based on the molecular level was proposed. Collagen alpha-1(I) chain, collagen alpha-2(I) chain and collagen alpha-1(III) chain degraded dramatically under the action of high temperature, leading to the collapse of the triple helix structure, which caused distortions and breaks of the fibrils. As a result, the collagen fiber bundles became tangled and bifurcated, leading to the orderly and tough collagen fiber network becoming disordered and dried out. In addition, a novel quantifiable indicator for assessing the degree of leather deterioration based on hydroxyproline content was proposed. These findings provide new insights into the study of deterioration mechanism and preventive conservation of archaeological leather excavated in dry areas.